Shannon dominated the opening half and two penalties from Tadhg Bennett and a conversion of a try by James Murphy gave them a 13-3 interval lead. Robbie Bourke replied with a penalty for Bohes.
A drop goal by Bennett and a try by John Shine extended Shannon's advantage to 21-3.
Bohes rallied and a try by John Sutton started their comeback. Bourke kicked three penalties to leave four between the sides. A second try by Bourke put the holders 22-21 in front.
Back came Shannon and with the last kick of the game Bennett converted a penalty to give Shannon victory and the first silverware of the new season.